GH-34577 [Python] Expose eol and null_value csv WriteOptions

[MartinNowak]

Rationale for this change

Expose remaining csv write options to pyarrow.

What changes are included in this PR?

Adding eol and null_string to csv.WriteOptions.

Are these changes tested?

Yes, testing of setters included.

Are there any user-facing changes?

This PR includes breaking changes to public APIs. (If there are any breaking changes to public APIs, please explain which changes are breaking. If not, you can remove this.)

This PR contains a "Critical Fix". (If the changes fix either (a) a security vulnerability, (b) a bug that caused incorrect or invalid data to be produced, or (c) a bug that causes a crash (even when the API contract is upheld), please provide explanation. If not, you can remove this.)

• GitHub Issue: [R][Python] Expand coverage of and align R/Python to C++ CSV WriteOptions #34577

[github-actions]

⚠️ GitHub issue #34577 has been automatically assigned in GitHub to PR creator.

[AlenkaF]

Thank you for submitting a PR!
There are some fixes needed for the CI to pass:

• Linter error:
  python/pyarrow/tests/test_csv.py:363:89: E501 line too long (119 > 88 characters)
• Python builds error:
  pyarrow/_csv.pyx:1431:34: Object of type 'CCSVWriteOptions &' has no attribute 'eol'
  -> CCSVWriteOptions will need to be updated in the libarrow.pxd